The present invention relates to a storage device and, more particularly, to a storage device which realizes fast access for data readout by use of a memory unit whose access time is relatively long.
A period of time necessary for data to be actually read or written after the start of a memory read or a memory write control is generally referred to as an access time. As regards modern semiconductor storages such as random access memories (RAMs), the average access time is approximately 200 nanoseconds. In a computer, programs and data are sequentially read out of a storage to perform operations based on the programs and data and, hence, the data processing rate is significantly effected by the memory access time. In light of this, a computer intended for fast processing uses a special storage whose access time is short. However, this type of high-speed storages are extremely expensive.